Water Prehydrolysis Research Articles

Kraft pulping of softwood chips with mild hot water pre-hydrolysis to understand the effects of wood chip thickness

Hemicelluloses consume alkali during kraft pulping and dissolve in the black liquor as a low energy fuel. Acidic pre-hydrolysis of softwood chips removes hemicelluloses but preserves cellulose content prior to pulping. This study compared mild pre-hydrolysis (140 °C) kraft pulping with conventional kraft pulping of commercial softwood chips at two H-factors for wood chips with thickness ranging from less than 2 mm to over 6 mm. The chip thickness less than 2 mm increased hemicelluloses oligomer yield and showed little influence on pulp fiber yield. However, the kraft pulp fiber length decreased 5.6%. Kappa number and fiber reject increased dramatically when chip thickness was greater than 6 mm. The detailed compositional analysis of kraft pulp and fiber quality analysis indicate that pre-hydrolysis followed by kraft pulping enhanced delignification with limited reduction of fiber length and width, and increased kinks. Strategic considerations for the integration of pre-hydrolysis into kraft pulping for future biorefineries were outlined.

Characterization of enzyme-resistant xylooligosaccharides extracted from hardwood chips by pre-hydrolysis and further depolymerized by enzymatic treatment

AbstractXylose-rich solutions were produced by applying water pre-hydrolysis on mixed hardwood chips followed by an enzymatic treatment of the filtrate. The liquid phase obtained after water pre-hydrolysis contained xylose and xylans as the major components as well as other hemicelluloses and monosaccharides, acetic acid, and some degradation products of the monosaccharides [furfural, 5-(hydroxymethyl)furfural]. This hydrolysate underwent a two-step enzymatic treatment successively with endo-1,4-β-xylanase and 1,4-β-xylosidase to specifically depolymerize xylans into xylose without producing monosaccharides from the other oligosaccharides. After this treatment, 20.5% of the xylose units remained as oligomers. Matrix-assisted laser desorption ionization time-of-flight (MALDI-ToF) mass spectrometry was applied after each step of the treatment to approach the structure of hemicellulose oligomers, to follow their depolymerization and to understand the reason for the resistance of some of them to enzymatic hydrolysis. It was found that highly acetylated xylans and/or xylans still substituted with 4-O-methylglucuronic groups were particularly resistant to this treatment.

Recycling of pre-hydrolysis liquor to improve the concentrations of hemicellulosic saccharides during water pre-hydrolysis of aspen woodchips

In this study, the pre-hydrolysis liquor (PHL) was recycled during aspen chip water pre-hydrolysis, and the effects of PHL recycling on the extraction and accumulation of the hemicellulosic saccharides especially that with high molecular weight in the PHL were studied. The results showed that the concentration of hemicellulose saccharides in PHL depended on the pre-hydrolysis temperature and PHL recycling times. Compared to the unrecycled PHL, the concentration of hemicellulosic saccharides in PHL increased significantly when recycling PHL once or twice at 170°C. Furthermore, the amount of high-molecular-weight hemicelluloses (HMHs) in PHL recycled once at 170°C increased from 2.58g/L (unrecycled) to 6.18g/L, but the corresponding average molecular weight of HMHs decreased from 9.2kDa to 7.6kDa. The concentration of hemicellulosic saccharides in PHL decreased with PHL recycling time at 180°C, accompanied by the formation of a significant amount of furfural.

Research on the Dissolution of Pentosans during Eucalyptus Hydrolysate Pretreatment

Hydrolysate pretreatment (HP) uses hot water pre-hydrolysis liquor (HWPL) as partial or full pretreatment medium for biomass. Pentosan dissolution during Eucalyptus HP was studied under holding times between 0 min and 160 min, holding temperatures between 150 °C and 190 °C, a hot water pre-hydrolysate ratio (HWPR) from 20% to 100%, and a fixed liquid to wood ratio of 1:6. Both the pentosan removals in the hydrolysate pretreated solid (HPS) and the hydrolysate pretreatment liquor (HPL) pento-saccharides contents were determined and compared with those of hot water pre-hydrolysis (HWP). When compared to HWP, the HP enhanced pentosan removal from the solid phase, and enriched the saccharides or promoted the in-situ conversion of saccharides into other chemicals in the liquid phase. Pentosan removal in the HPS increased when holding time and temperature were increased. Increasing holding time first increased the pento-saccharide content in the HPL, and then decreased it after reaching the maximum. Elevating the holding temperature increased the pento-saccharide content in the HPL, except for arabino-oligosaccharide. Different HWPR had varying influences on pentosan removal in the HPS and on the saccharides concentration in the HPL. When controlled, HP positively influenced hemicellulose removal from biomass, and increased utilization value of the liquid phase obtained post pretreatment.

Properties of cellulose nanocrystals from oil palm trunk isolated by total chlorine free method

Cellulose nanocrystals were isolated from oil palm trunk by total chlorine free method. The samples were either water pre-hydrolyzed or non-water pre-hydrolyzed, subjected to soda pulping, acidified and ozone bleached. Cellulose and cellulose nanocrystal (CNC) physical, chemical, thermal properties, and crystallinity index were investigated by composition analysis, scanning electron microscopy, transmission electron microscopy, fourier transform infrared, thermogravimetric analysis and X-ray diffraction. Water pre-hydrolysis reduced lignin (<0.5%) and increased holocellulose (99.6%) of ozone-bleached cellulose. Water pre-hydrolyzed cellulose exhibited surface fibrillation and peeling off after acid hydrolysis process compared to non-fibrillated of non-water pre-hydrolyzed cellulose. Water pre-hydrolysis improved final CNC crystallinity (up to 75%) compared to CNC without water pre-hydrolysis crystallinity (69%). Cellulose degradation was found to occur during ozone bleaching stage but CNC showed an increase in crystallinity after acid hydrolysis. Thus, oil palm trunk CNC can be potentially applied in pharmaceutical, food, medical and nanocomposites.

Quality evaluation of dissolving pulp fabricated from banana plant stem and its potential for biorefinery

The study was conducted to evaluate the quality of dissolving pulp of Musa sapientum L. (banana) plant stem and its potential for biorefinery. Introduction of pre-hydrolysis prior to any alkaline pulping process helps to reduce the content of hemicellulose and consequently produce acceptably high content of cellulose pulp. Water pre-hydrolysis was done at 150°C for 90min. The amount of lignin, xylan and glucan in the extracted pre-hydrolysis liquor (PHL) was 1.6, 4.9 and 1.6%, respectively. Pulping of pre-extracted chips was done following soda-AQ, alkaline sulfite and kraft process. The ratio of chip to liquor was 1:7 for both pre-hydrolysis and pulping. The kraft pulping process with 20% active alkali and 25% sulfidity at 150°C for 90min showed the best result. The lowest kappa number was 26.2 with a considerable pulp yield of 32.7%. The pulp was bleached by acidic NaClO2 and the consistency was 10% based on air-dried pulp. The lowest amount of 7% NaClO2 was used for the bleaching sequence of D0ED1ED2. After D0ED1ED2 bleaching, the pulp showed that α-cellulose, brightness and ash were 91.9, 77.9 and 1.6% respectively. The viscosity was 19.9cP. Hence, there is a possibility to use banana plant stem as a raw material for dissolving grade pulp and other bioproducts.

A Fresh Look at the Kinetics of Pentosan Removal from Lignocellulosic Biomass

The effect of time, temperature and concentration of prehydrolyzing agent on the biomass prehydrolysis have been studied for pentosan removal. Basic kinetic parameters i.e. rate constant, order of reaction, energy of activation and frequency factor were calculated. This study on the kinetics of pentosan removal reveals that the rate of pentosan removal does not follow exactly first order kinetics and shifting of order is observed during the reaction. In searching for a kinetic equation for pentosan removal, it was found that the data was well fitted by an order at higher concentration and by another order at lower concentration of prehydrolyzing agent. The order of reaction of pentosan removal lies between 0.8 to 1.40. A regression model was developed for % pentosan removal relating to temperature and time for water prehydrolysis at higher temperatures. This model was well fitted by data given in literature.

Water Prehydrolysis of Birch Wood Chips and Meal in Batch and Flow-through Systems: A Comparative Evaluation

Water prehydrolysis can be used as a pretreatment to extract hemicelluloses and lignin from biomass prior to its conversion into value-added products. In this study, the effects of operational conditions such as reactor system, flow, particle size, and solids content during prehydrolysis of birch wood are compared, using the wood yield as indicator of pretreatment intensity. The results show that both batch and flow-through (FT) systems are equally effective in removing the carbohydrates from the wood. Increasing flow and decreasing particle size and solids content, however, facilitate the removal of lignin. This increased delignification is partly related to a lower extent of condensation reactions. A FT system is also advantageous for the recovery of the extracted sugars because degradation reactions are minimized. Furthermore, by applying elevated temperatures and short retention times, the sugars concentration in the hydrolysate might be only somewhat higher than that in a batch system.

Water Prehydrolysis of Moso Bamboo Dissolving Pulp

The chemical comcomposition and water prehydrolysis of moso bamboo were studied to prepare high grade dissolving pulp. The results indicated that the moso bamboo was an appropriate none-wood material for great dissolving pulp goten as its high cellulose content. By single factor method, the optimum prehydrolysis conditions which were 150°C, 120minutes and 1:8 of liquor-to-wood tatio, were obtained. Based on the optimum conditions, the yield was 90.35%, and the retention rate of cellulose, pentosan, acid accumulator insoluble lignin, and ash were respectively 96.30%, 88.22%, 88.13%, and 11.71%.

Sugar cane bagasse prehydrolysis using hot water

Results are presented on the hot water prehydrolysis of sugar cane bagasse for obtaining ethanol by fermentation. The experimental study consisted of the determination of the effect of temperature and time of prehydrolysis on the extraction of hemicelluloses, with the objective of selecting the best operating conditions that lead to increased yield of extraction with a low formation of inhibitors. The study, carried out in a pilot plant scale rotational digester, using a 32 experimental design at temperatures of 150-190oC and times of 60-90 min, showed that it is possible to perform the hot water prehydrolysis process between 180-190oC in times of 60-82 min, yielding concentrations of xylose > 35 g/L, furfural < 2.5 g/L, phenols from soluble lignin < 1.5 g/L, and concentrations < 3.0 g/L of hemicelluloses in the cellolignin residue. These parameters of temperature and prehydrolysis time could be used for the study of the later hydrolysis and fermentation stages of ethanol production from sugar cane bagasse.

Bioconversion of a mixture of paper sludge and extraction liquor from water prehydrolysis of Eucalyptus chips to ethanol using separate hydrolysis and fermentation

Paper sludge and extraction liquor from water prehydrolysis of Eucalyptus chips before pulping are potential raw materials for ethanol production in an integrated forest biorefinery concept. Ethanol production from paper sludge, extraction liquor from water prehydrolysis of Eucalyptus chips, and a mixture of both using separate hydrolysis and fermentation were investigated. The hydrolysate composed of 51.01±0.72 g/L glucose, 30.11±0.09 g/L xylose, and 13.65±0.94 g/L cellobiose, which was obtained by enzymatic saccharification of the mixture at an initial consistency of 6% (w/v, expressed in terms of total carbohydrate mass), was used for ethanol production by yeast SHY07-1 without prior detoxification and nutrient supplementation. A final ethanol concentration of 36.82±0.35 g/L was achieved, corresponding to an ethanol yield of 0.45±0.04 g/g with a fermentation efficiency of 80.71±0.03% and an ethanol productivity of 0.31±0.01 g/(L h). This confirmed the feasibility of co-fermentation of these two materials for bioconversion to ethanol.

Purification of Eucalyptus globulus water prehydrolyzates using the HiTAC process (high-temperature adsorption on activated charcoal)

Abstract The implementation of biorefinery concepts into existing pulp and paper mills is a key step for a sustainable utilization of the natural resource wood. Water prehydrolysis of wood is an interesting process for the recovery of xylo-oligosaccharides and derivatives thereof, while at the same time cellulose is preserved to a large extent for subsequent dissolving pulp production. The recovery of value-added products out of autohydrolyzates is frequently hindered by extensive lignin precipitation, especially at high temperatures. In this study, a new high-temperature adsorption process (HiTAC process) was developed, where lignin is removed directly after the autohydrolysis, which enables further processing of the autohydrolyzates. The suitability of activated charcoals as a selective adsorbent for lignin under process-relevant conditions (150 and 170°C) has not been considered up to now, because former experiments showed decreasing efficiency of charcoal adsorption of lignin with increasing temperature in the range 20–80°C. In contrast to these results, we demonstrated that the adsorption of lignin at 170°C directly after autohydrolysis is even more efficient than after cooling the hydrolyzate to room temperature. The formation of lignin precipitation and incrustations can thus be efficiently prevented by the HiTAC process. The carbohydrates in the autohydrolysis liquor remain unaffected over a wide charcoal concentration range and can be further processed to yield valuable products.

Digestibility and paper-making properties of prehydrolyzed softwood chips

The effect of hemicellulose extraction of pine wood chips by water prehydrolysis on subsequent kraft cooking and paper properties was studied. Prehydrolysis reduced the required cooking time by approximately 40% and increased kappa number reduction in oxygen delignification. Prehydrolysis decreased the overall brownstock pulp yield on wood by 7.2 percentage units. Consequently, valuable products would need to be produced from the prehydrolyzate to compensate for the resulting increase in wood consumption. In DED-bleaching, lower bleaching chemical dosages were needed with prehydrolyzed than with unhydrolyzed pulps to obtain similar final brightness. As expected, removal of hemicelluloses led to a decrease in the tensile index and increase in the tear index. At a given density, the strength potential of prehydrolyzed pulps was higher than that of unhydrolyzed pulps. There was an up to more than fivefold increase in beating revolutions in a PFI-mill needed to obtain comparable tensile indices. This significant reduction in beating response might pose problems in the commercialization of prehydrolyzed pulps. In general, differences between the paper properties of prehydrolyzed pulps and unhydrolyzed pulps are attributed to decreased inter-fiber bonding in prehydrolyzed pulps.

The relationship between two methods for evaluating five-carbon sugars in eucalyptus extraction liquor

Alkaline pre-extraction and hydrothermal hydrolysis were carried out with eucalyptus chips. Two methods were used to determine and calculate the extraction yield of five-carbon sugars. One is an indirect method, based on the difference of pentosan content between the chips before and after pre-extraction. The other method is to directly measure the content of five-carbon sugars in the extracting solution. The results indicated that there was a defined relationship between the two methods. For alkaline pre-extraction, a good logarithmic relationship was shown. There was a good linear relationship for hot water prehydrolysis. So the pentosan content of the extracted chips could be predicted from the results of the latter method, referring to the two relational expressions. In this study, a simple and rapid method of spectrophotometry was introduced, which will help in the evaluation of extraction yield of five-carbon sugars during biomass processing.

Effect of autohydrolysis of Eucalyptus globulus wood on lignin structure. Part 1: Comparison of different lignin fractions formed during water prehydrolysis

Abstract The effect of autohydrolysis of Eucalyptus globulus wood was studied with regard to conditions applied in a prehydrolysis-kraft process on the physico-chemical properties of lignin obtained in both the wood residue and hydrolysate. As a reference, milled wood lignin (MWL) was isolated from native wood and compared to three lignin fractions formed during prehydrolysis: 1) lignin from the wood residue isolated as MWL, 2) lignin precipitated from the prehydrolysate during cooling and separated by centrifugation, and 3) lignin degradation products soluble in the prehydrolysate extracted with ethylacetate. All lignin fractions were subjected to Fourier transform infrared (FTIR) spectroscopy, methoxy group determination, elemental analysis, size exclusion chromatography and quantitative nuclear magnetic resonance (NMR) spectroscopy. The results indicate that extensive lignin degradation occurs during prehydrolysis through homolytic cleavage of the aryl-ether bonds resulting in a substantial molecular weight loss of the residual lignin in the treated wood and in the lignin fractions isolated from the prehydrolysate. The aryl-ether cleavage is coupled with a strong increase in phenolic hydroxyl groups and a decrease in aliphatic hydroxyl groups. Indication for condensation reactions were found by NMR spectroscopy.

Process for the production of dissolving pulp from Trema orientalis (nalita) by prehydrolysis kraft and soda-ethylenediamine (EDA) process

This paper presents a preliminary study for the production of dissolving pulp from Trema orientalis (Nalita). Water prehydrolysis kraft and soda-ethylenediamine (EDA) pulping for the production of dissolving pulp from T. orientalis was investigated. Prehydrolysis at 150 and 170 oC did not produce pulp with high α-cellulose content when using the kraft process. But addition of 0.25 % H2SO4 in prehydrolysis liquor increased the purity of the pulp with the sacrifice of pulp yield and viscosity. The soda-EDA process produced better pulp yield, kappa number, viscosity, and α-cellulose content as compared to the kraft process. Increasing EDA charge in the soda liquor increased pulping selectivity and α-cellulose content. Degraded cellulose (R18-R10) in soda-EDA pulp was lower than kraft pulp. But the bleachability of soda-EDA pulp was inferior as compared to kraft pulp in DED bleaching.

Positive and negative aspects of soda/anthraquinone pulping of hardwoods

The positive aspects of the non-sulfur soda/anthraquinone (SAQ) process are mostly tied to improved energy efficiency while lower pulp brightness after bleaching is its most significant drawback. A credible method that quantifies bleachability as well as an approach that solves the problem for SAQ pulps from hardwoods will be described. A straight line correlation ( R 2 = 0.904) was obtained between O 2 kappa number and final light absorption coefficient (LAC) value after standardized OD 0E pD 1 bleaching of nine hardwood kraft pulps from three laboratories and one pulp mill. The bleachability of pulps from four different soda processes catalyzed by anthraquinone (AQ) and 2-methylanthraquinone (MAQ) was compared to that of conventional kraft pulps by comparing O 2 kappa number decrease and final LAC values. It was observed that a mild hot water pre-hydrolysis improved the bleachability of SAQ pulps to a level equal to that of kraft.

Effect of various steps of purification on ash content and ash constitution of cellulose. II. Cellulose prepared from sugar-cane bagasse

The effect of the various steps of purification on the ash content and ash constitution of cellulose prepared from bagasse has been examined. After each step of purification, samples were analysed for total ash, SiO2, Ca, Fe and Mn. Two schemes of purification have been investigated. The first involves acid prehydrolysis, alkaline pulping and bleaching, and the second water prehydrolysis, acid pulping and bleaching. The first scheme has a better effect in diminishing the ash content, and gives a pulp containing 95.8% alpha cellulose with a 90% degree of whiteness.

Effect of various steps of purification on ash content and ash constitution of cellulose. II. Cellulose prepared from sugar‐cane bagasse

AbstractThe effect of the various steps of purification on the ash content and ash constitution of cellulose prepared from bagasse has been examined. After each step of purification, samples were analysed for total ash, SiO2, Ca, Fe and Mn. Two schemes of purification have been investigated. The first involves acid prehydrolysis, alkaline pulping and bleaching, and the second water prehydrolysis, acid pulping and bleaching. The first scheme has a better effect in diminishing the ash content, and gives a pulp containing 95.8% alpha cellulose with a 90% degree of whiteness.

Southern pineprehydrolyzates: Characterization of polysaccharides and lignin fragments

AbstractPrehydrolyzates obtained by treatment of southern pine chips at 175° with steam and water were examined in parallet studies. Carbohydrates were separated from other solids and fractionated into monosaccharides, low‐molecular weight polysaccharides and highmolecular weight polysaccharides. The latter fractions were selectively subfractionated into series of glucomannans and galactoglucomannans using barium precipitation. The poly‐saccharide fractions were characterized by gel permeation chromatography (gpc), the hemicellulose subfractions by periodate oxidation, vapor pressure osmometry, polarimetry, and end‐group assay. Sugar ratios were determined on hydrolyzates of all fractions. Water prehydrolysis was shown to remove substantially more carbohydrates from the chips than steam prehydrolysis, 9.3% versus 3.3% (O.D. wood basis), and these carbohydrates had higher average molecular weight, contained more mannose per unit glucose and yielded more galactoglucomannans than those removed by steam. One of the galactoglucomannans from water prehydrolyzate had the highest number average molecular weight in this study: 3100 by end‐group assay, 3800 by osmometry; polysaccharides of even higher molecular weight were indicated by gpc prehumps. Several monomeric lignin degradation products were identified in the methyl ethyl ketone soluble fraction of steam prehydrolyzate. Among these were coniferaldehyde, vanillic acid, vanillin, protocatechualdehyde, phydroxybenozic acid and, unexpectedly, a sizeable proportion of dihydroconiferyl alcohol.